Consider a wireless mobile local area network environment supporting many low power, portable, personal computers or communication devices. The portable personal computers are assumed to support a host of communication services with high data rate applications ranging from interactive data with voice capability to multimedia. The geographical area is divided into small cells for two major reasons. Firstly, the power limitations of mobile terminals dictate the maximum range of wireless communication. Secondly, smaller cells allow greater spatial reuse of the communication bandwidth than larger cells. Associated with each cell there is one base station and time-varying population of mobile stations. This structure, see FIG. 1, lends itself to a cellular architecture in which mobile and base stations communicate over a wireless channel. The base stations communicate amongst themselves via by some stationary high-speed backbone networks. As an example, consider the environment of an industrial campus consisting of several office buildings. The buildings are divided into cells and cells are connected via some backbone network such as a wired LAN. Portable terminals can operate both indoor and outdoor with limited range (e.g, 50 meters) and have wireless access to the base stations on the backbone network. Each wireless channel in the network is shared by many mobile stations. In addition, in areas where cells of different base stations overlap, the wireless channel is shared by two or more base stations. Thus, in order to enable reliable and efficient communications between the mobile stations and the fixed backbone network, a multiaccess protocol must be employed.
In general, any multiaccess scheme for cellular networks can be divided into the intercell tier and intracell tier. The intercell tier ensures that transmissions of users from different cells within each subnetwork (e.g, LAN, WAN) do not interfere with each other. This tier of the multiaccess scheme is essentially a coordination among the base stations. The intracell tier ensures that within each cell of the network, the transmissions of all users that are within the same cell do not interfere with each other. This tier of the multiaccess scheme is essentially a coordination among mobile users that are within the same cell.
A problem in such environments is as follows. A basic constraint in every wireless communication system is that the total available spectrum, which determines the communication capacity of the system, is given and fixed. For example, the FCC regulates the spectrum usage in the United States. The problem is how to allocate bandwidth for each cell and for each user on a demand-driven basis, such that (i) the aggregate throughput, and (ii) the available peak-rate per user, are both maximized.
The well-known solutions in the prior art fall into one of two categories. The first category is FDMA [3, 6], wherein two neighboring cells always get distinct frequency bands in which to communicate between the base stations and the mobile units. Reference [6] is hereby incorporated by reference. The limitation of this solution is that the communication bandwidth may be too small in order to get a sufficient number of distinct frequency bands. The second category is TDMA [3, 4, 6], wherein all cells share the same frequency band and the transceivers in two neighboring cells are never simultaneously active. The limitation of this solution is that every transceiver has to communicate at a prohibitively high rate for a short period of time, which causes coordination problems between neighboring cells. A desirable solution is one which avoids the above-mentioned limitations. References [1, 3, 5, 7] describe related work on intracell multiaccess schemes for wireless networks.
U.S. Pat. No. 5,185,739 to Spear discloses a method for efficiently utilizing frequency frames by sharing frames of a particular frequency among base stations. However, the allocation described in Spear is fixed and not demand driven.
U.S. patent application, Ser. No. 785,643, corresponding to IBM Docket No. YO991-148, filed on Oct. 31, 1991 by the assignee of the current application, allowed Nov. 3, 1992, issuing into U.S. Pat. No. 5,210,753 on May 11, 1993, discloses the determination of a maximum set of independent cells which are initially activated while other cells not in this independent set are placed in a waiting state.
U.S. patent application Ser. No. 07/850,541, corresponding to IBM Docket No. YO991-117, filed on Mar. 13, 1992 by the assignee of the current application discloses a method of determining controlling base stations in overlapping cells.
U.S. Pat. No. 4,144,411 to Frenkiel discloses a method of allocating frequency channels in cellular network with cells of varying sizes.
U.S. Pat. No. 5,093,925 to Chanroo discloses the assignment of frequencies for telephone connections in a three dimensional layout to minimize co-channel interference.
U.S. Pat. No. 3,632,885 to Herold discloses how a ground station can transmit data on a channel associated with another ground station when that ground station is not transmitting on its own channel.
U.S. Pat. No. 4,949,395 to Rydbeck discloses a method of dynamically allocating time slots at the intracell level, and not at the intercell level.
U.S. Pat. No. 5,029,165 to Choi et al discloses the notion of clusters of signal links associated with a common channel type transfer point in a common channel signalling system.
Japanese patent application 63-298775 to Atsushi Murase discloses a multiple radio zone mobile communication system wherein a service area is covered simultaneously by a number of small radio zones and a large radio zone with each zone having its own base station.